Seed dormancy and germination of the basal eudicot family Ranunculaceae from a world vegetation and phylogenetic perspective

Abstract As part of our on-going inquiry into how the kinds of seed dormancy in flowering plant families are distributed geographically and phylogenetically, we have reviewed the Ranunculaceae. The family has c. 2525 species in 50 genera and five subfamilies (Coptidoideae, Glaucidioideae, Hydrastidoideae, Ranunculoideae and Thalictroideae) and mostly grows in temperate regions. It has many herbaceous perennials that are dormant for part of the year, as well as annuals and vines ( Clematis ). Seeds have a small/underdeveloped linear or rudimentary embryo and thus morphological (MD) or morphophysiological (MPD) dormancy. MD is found in Coptidoideae, Ranunculoideae and Thalictroideae, whereas MPD is found in all subfamilies. Ranunculoideae is the most common subfamily and occurs in two tropical and nine temperate world vegetation regions. All nine known levels of MPD are found in the Ranunculaceae. The levels of MPD that occur in five or more vegetation regions are nondeep simple, deep simple, intermediate complex and deep complex, and vegetation regions with five or more levels are matorral, deciduous forest, steppe, boreal/subalpine and Arctic/alpine. Regardless of the level of MPD, seeds of spring-germinating species germinate after being cold-stratified. However, some seeds with nondeep simple MPD, in which the physiological dormancy component of MPD is broken during summer, germinate in autumn. The presence of more than one level of MPD in a vegetation region may represent past migrations of lineages (with different levels of MPD) from areas with cold winters to new areas with cold winters.